1. Field of the Invention
The present invention is related to a rotary combustor, or incinerator, for waste material and, more particularly, to automatic control of combustion gas supplied to a rotary combustor.
2. Description of the Related Art
Proper disposal of solid waste has become an increasingly serious problem as existing sites for land disposal near capacity and new sites become increasingly difficult to locate while the amount of toxic chemicals, particularly in municipal waste, appears to be increasing. Incineration of combustible solid waste has long been used to reduce the quantity of solid matter needing disposal. However, existing methods of incineration often result in incomplete combustion and produce exhaust gases which include carbon monoxide and unburned hydrocarbons.
One device which is used for incinerating municipal solid waste is known as a water-cooled rotary combustor. Examples of water-cooled rotary combustors are described in U.S. Pat. Nos. 3,882,651 to Harris et al.: 4,066,024 to O'Connor; and 4,226,584 to Ishikawa. A general description of a rotary combustor is provided immediately below and a more detailed description will be provided later.
As illustrated schematically in a cross-sectional side elevational view in FIG. 1A, a water-cooled rotary combustor generally includes a combustion barrel 10 having a generally cylindrical side wall 36 affixed to annular support bands 13 which are received on rollers 12 to permit rotation of the barrel 10 about its longitudinal axis. The barrel 10 has a generally open input end 16 for receiving material to be burned, such as municipal solid waste 14 which varies in moisture content and heating value. A second or exit end 18 of the barrel 10 is disposed in a flue 19. Exhaust gases 20 and solid combustion products 22, i.e., ash, exit the combustion barrel 10 at the exit end 18. The barrel 10 is cooled by cooling pipes 24 joined by gas-porous interconnections 25 to form the generally cylindrical side wall 36 of the barrel 10. Due to the variable nature of municipal solid waste, it is difficult to maintain a constant feed rate of the waste into and through the barrel 10, and thus the location and strength of the fire 26 in the barrel 10 varies over time. As a result, the constitution of the exhaust gases 20 varies widely over time as illustrated in FIG. 2 with respect to percentage of oxygen. Such variation is an indication that the waste material 14 is burning unevenly.